Thin-film batteries (TFBs) typically may require a high-performance hermetic encapsulation that protects them against ambient chemical reactants (such as, for example, O2, H2O, N2, CO2, etc.) over many years of life time. The quality requirements for the encapsulation may be independent of the material choice of the most sensitive component in a thin-film battery, the anode (metallic lithium, lithium-ion [e.g. carbon or tin nitride], or “Li-free” anode [=current collector at which metallic lithium is plated out during TFB operation]), because any of these anodes may cease to work after a comparable amount of long-term, accumulated transmission of reactants into the TFB. For a 10-year shelf-life expectancy, for instance, the encapsulation should preferably exhibit a water vapor transmission rate (WVTR) of less than 10−3 g/m2-day while the oxygen transmission rate (OTR) should preferably be smaller than 5×10−4 g/m2-day. These estimated quantities are based on the complete reaction of 1.6×10−4 g/cm2 of lithium metal or lithium ions in the anode to either LIOH or Li2O. Furthermore, these estimated quantities represent practical rates and include reactants ingress (transmission) along the encapsulation-TFB seal area, in addition to the typical transmission rates that are measured only vertically through the encapsulation by the MOCON method.
However, current non-thin-film encapsulation is generally responsible for nearly 50% or more of the overall thickness of standard TFBs. When adjoining TFBs into a battery stack for applications for which the supply of a maximum of energy within a given thickness is critical, one can not afford to waste 50% of the stack volume on non-energy providing encapsulation.
Thus, a need exists for the encapsulation thickness to be reduced to a minimum without compromising the protection performance.